It is known to use liquid ammonia to produce work. The liquid ammonia is evaporated at the bottom of a large closed system such that the vapors flow up to the upper, cool end of this system where they are condensed. This condensate flows down to the hot bottom of the system through a turbine or other such device which serves, water-mill fashion, to produce work from the falling liquid. Such a system requires a temperature differential of at least 20.degree.C in order to function and must be relatively large.
It is also known to evaporate a hydrocarbon such as propane having a low boiling point by means of warm surface sea water. The vapor propels a turbine and is condensed by cooler sea water drawn up from well below the surface, whereupon the condensate is again evaporated. Such an arrangement is frequently relatively bulky and requires considerable investment in equipment, along with a particular geographic location. Such power generation requires the turbine or the like to be moved directly by vapor and not by liquid. The condensed propane is pumped from the condenser to the vaporizer so the whole device is extremely large and very expensive.
The exploitation of geothermal energy also presents another potential source of power. This is done by simply driving a turbine with steam issuing from a steam well or the like, or by using the heat at several hundred meters below the surface to boil water. The generated steam is used to drive turbines. Since water has a relatively high evaporation entropy and a correspondingly low vapor pressure it is necessary to drive the turbine with the liquid. Since it is necessary to drill an extremely deep well to obtain a temperature of between and 130.degree.C the cost of such an installation is usually prohibitive.